1. Field of the Invention
The present invention relates to fuel injection systems for small utility engines. More particularly, the field of the invention involves actuators for fuel injectors in such small utility engines.
2. Description of the Related Art
Electronic fuel injection systems are known which utilize pulse width modulation to regulate fuel flow through an injector between a fuel pump and the manifold on the cylinder head. These type of systems are common in automotive applications, wherein an electronic timing control circuit delivers the pulse width modulated signal to the solenoid of the fuel injector. The timing control circuit is powered by the power system of the engine, initially by the engine battery until the alternator can provide a constant DC power source. However, such systems are not compatible with engines of small utility engines, such as for lawn mowers, garden tillers, and the like, as those small utility engines do not have a battery for the initial operation of the electronic timing control circuit.
One known fuel injection system overcomes this difficulty in applying fuel injection technology to small utility engines which do not have a battery. This known system comprises an ignition unit disposed radially outward adjacent to a magnet mounted to the external periphery of the flywheel. The ignition unit includes a built-in ignition coil for providing an induced current through a wire attached to the spark plug. The fuel injection system includes the flywheel which has a plurality of magnets mounted at its radially inward periphery. The flywheel rotates about a stator core having a plurality of windings around each pole projection. The magnets are electrically associated with stator projections for inducing a current in the winding. The output from the windings functions as an input to a power supply circuit for an electronic timing control circuit. The timing control circuit receives input signals from a crank angle sensor, an engine coolant temperature sensor, a throttle valve opening sensor, and an intake air temperature sensor. The timing control circuit controls both the start timing and the duration of operation for the fuel injection valve. The flywheel and stator define an AC generator providing power to the timing control circuit. The AC generator must be sized large enough to power the timing control circuit at a very low engine speed to facilitate starting of the engine. Additionally, the AC generator must supply enough power to energize the fuel injector at any time.
A difficulty with this known design involves the expense of providing the magnets, windings, and associated material which form the power supply circuit. Also, a separate sensor is required to provide the timing control circuit with information regarding the operating condition of the engine. This arrangement requires a significant increase in the amount of materials required to support and operate the timing control circuit. The increased amount of materials, and the additional sensors required, adds to the expense of the engine. Additionally, the weight of the engine is increased, which impairs the operation and/or efficiency of the small utility equipment.